Authorities are investigating if a shooting in Massachusetts of two Black people by a white man was a hate crime after racist messages were found in the suspect Nathan Allen’s handwriting.

According to the Associated Press, Suffolk County District Attorney Rachael Rollins said investigators came across “troubling white supremacist rhetoric” that expresses “anti-Semitic and racist statements againgst Black individuals" in Allen’s handwriting.

The 28-year-old has been identified as the man who shot and killed David Green, a retired Massachusetts State Police officer, and Romana Cooper, an Air Force veteran, after emerging from a stolen truck that he crashed into a building on Saturday afternoon (June 26).

Officials described Green and Cooper as innocent bystanders. Allen was fatally shot by police moments later.

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The shooter “walked by several other people that were not Black and they are alive. They were not harmed,” Rollins said to reporters Sunday, the AP reports. “They are alive and these two visible people of color are not. We will continue to look and see,” she said.

Details about what exactly the suspect wrote or where the writings were found were not made available to reporters, but Rollins did say that the investigation is in its early days and that the families of the victims “deserve answers and we will find out what happened here.”

Green worked in law enforcement for nearly 40 years. Police Col. Christopher Mason says he was shot outside his home.

“Trooper Green was widely respected and well-liked by his fellow Troopers, several of whom yesterday described him as a ‘true gentleman’ and always courteous to the public and meticulous in his duties,” Mason said in an emailed statement, according to the AP. “From what we learned yesterday, he was held in equally-high regard by his neighbors and friends in Winthrop.”

On Sunday, mourners gathered at the scene of the crime, leaving family near the destroyed building, the Boston Globe reports.